1. Field of the Invention
The invention relates to apparatus for maintaining a desired dimensional relationship between two surfaces when that apparatus is exposed to an environment consisting of wide variations in temperature.
2. Description of Prior Art
The ability to achieve and maintain a desired dimensional relationship between two surfaces has previously been achieved by electro-mechanical means, by thermal stabilization, and by temperature compensating structures.
The electro-mechanical methods require the use of temperature sensing devices, associated sensing and drive circuits and motors to move the position of one surface as a temperature change is sensed. The drawbacks involved with these methods are the cost, complexity, size, and weight penalties imposed by the motors, control circuitry, and associated structural mounts involved.
The thermal stabilization methods require that provisions such as thermal blankets and heaters be incorporated to essentially maintain an isothermal environment. In most cases where even a minimal temperature range is to be encountered, the power required and other problems with maintaining the ability to operate at high temperatures (limiting allowable insulation) make this approach infeasible.
The use of temperature compensating structures has permitted a limited amount of temperature compensation movement to be achieved in specific designs by varying the structural materials used in the housing containing the surfaces desired to be separated. Strength requirements of the housing structure involved normally limit the material selection to a narrow range of strong materials (e.g., stainless steel, invar, or aluminum) and each application must be highly individualized. In addition to the cost involved in each specialized housing design, the limited range of temperature related movement achievable normally results in less than optimum results.
Accordingly, it is an object of the present invention to provide a temperature compensating positioning device that has a combination of characteristics which will enable it to overcome the aforementioned disadvantages of the prior art devices and which make it particularly well suited to the requirements of avionic equipment. Such avionic equipment requirements which this novel invention can meet include small size, and weight, operability over a wide temperature range, and high reliability.